1. Field of the Invention
In general, this invention relates to automotive navigational mapping equipment and, more specifically, to a map display which utilizes a locking desired heading to control the orientation of an electronic map.
2. Description of the Related Art
Automotive navigational equipment utilizing map displays are common in the field of electronic navigation equipment. In general, these devices display a map of a desired area for a driver to reference while driving or planning a route. All such systems must implement some criteria for determining the orientation of the displayed map.
Some prior art systems always display the map heading north at the top of the electronic map display. These prior art systems may be useful in displaying an absolute direction of travel, but can become difficult to interpret while a vehicle is in motion. In such a situation, the user has to first locate the position of the vehicle on the map, determine the current direction the vehicle is traveling, and then reference the direction relative to the map display.
Some other types of navigational systems utilize positioning sensors, such as Global Positioning Systems (GPS antenna/receivers), to constantly calculate a vehicle's direction and use this calculated direction as the top of the display. Because some GPS systems become inaccurate at low speeds, the inaccuracies can cause the map display to shift erratically, confusing and annoying the driver attempting to read the map directions. In addition, since most turns from one road onto another occur at low velocity, the shifting of the map can become extremely disorienting to the driver at a time when it is most needed.
Some known prior art systems have attempted to remedy these problems by incorporating a desired heading, or desired track, to fix the orientation of the map display. This desired track method locates the general directional heading of the entire route and fixes that direction as top of the display for the entire trip. However, this method can become difficult to use, especially when there are multiple heading changes along a route. For example, in planning a route, the general direction of the entire route may be east. According to the prior art desired track method, the map display would be orientated so that east would always be at the top of the display. If the route being taken is generally straight east, the desired heading method generally serves its purpose. The desired track becomes disorientating, however, if the route changes direction either as multiple thoroughfares are traversed or just change in thoroughfare direction. In this scenario, east might be displayed as top while the vehicle may be traveling a different direction, thereby eliminating the usefulness of a desired track heading.
There exists a need for a map heading display which determines a map orientation that is useful in accommodating the relative current direction of a vehicle without being inaccurate and unsteady at low speeds and which is able to account for variations in the direction of travel along a desired route.